1. Technical Field
This disclosure relates generally to an ignition coil working to produce an electric spark in a spark plug for use in internal combustion engines.
2. Background Art
Typical ignition coils for spark plugs installed in internal combustion engines are equipped with a high-voltage connector terminal which connects at an end thereof with a trailing end of a winding of a secondary coil and is placed in elastic abutment with a high-voltage output terminal disposed in a lower portion of a holder casing. An electric circuit, which extends from the trailing end of the secondary coil, to the high-voltage connector terminal, to the high-voltage output terminal, and to the spark plug, works to apply the high voltage to the spark plug.
Japanese Patent First Publication No. 2004-207582 discloses the above types of high-voltage connector terminal and high-voltage output terminal of the ignition coil. In order to ensure the stability in elastic contact between the high-voltage connector terminal and the high-voltage output terminal, the high-voltage output terminal has irregularities formed on an end surface thereof. Specifically, the irregularities increase an area of contact between the high-voltage connector terminal and the high-voltage output terminal to enhance the stability in elastic contact therebetween.
The above structure of the high-voltage output terminal, however, faces the drawback in that rubbing of the high-voltage connect terminal against the irregularities on the high-voltage output terminal facilitate ease of wear of the irregularities, which may lead to adhesion of foreign objects thereto, that is, contamination of surfaces of contact between the high-voltage connector terminal and the high-voltage output terminal. Such contamination results in instability of electric contact between the high-voltage connector terminal and the high-voltage output terminal and also accelerates the wear of them. The foreign objects may also be adhered to the secondary coil, thus resulting in a decrease in resistance thereof to voltage and degradation in reliability of operation of the ignition coil. Further, when the high-voltage connector terminal is disposed at an inclined orientation on the high-voltage output terminal during assembling processes of the ignition coil, it may cause the top of the high-voltage connector terminal to get stuck to the surface of the high-voltage output terminal, so that the high-voltage connector terminal may deform, which leads to damage to a bobbin of the secondary coil by which the high-voltage connector terminal is retained or lack in pressure required to ensure the stability in contact between the high-voltage connector terminal and the high-voltage output terminal.